Ammonium arsenates,organo-substituted arsenates,and sodium,potassium and calcium arsenite as first stage catalytic additives in direct esterification process



United States Patent 3,496,145 AMMONIUM ARSENATES, ,ORGANO-SUBSTI- TUTEDARSENATES, AND SODIUM, PO- TASSIUM AND CALCIUM ARSENITE AS FIRST STAGECATALYTIC ADDITIVES IN DIRECT ESTERIFICATION PROCESS Mary E. Carter,Philadelphia, and -John A. Price, Swarthmore, Pa., assignors to FMCCorporation, Philadelphia, Pa., a corporation of Delaware No Drawing.Filed June 26, 1967, Ser. No. 648,951 Int. Cl. C08g 17/06 US. Cl. 260-75Claims ABSTRACT OF THE DISCLOSURE Process of preparing polyethyleneterephthalate resin comprising carrying out a direct esterificationreaction between terephthalic acid and ethylene glycol in the presenceof an arsenic compound, wherein the arsenic compound is selected fromthe group consisting of ammonium arsenate, diammonium arsenate, disodiummethyl arsenate, sodium dimethyl arsenate, calcium arsenite, potassiumhydrogen arsenite, sodium arsenite, and disodium arseno-acetatemonohydrate.

This invention relates to a method of preparing highly polymeric linearpolyesters. In particular, it relates to a novel method of preparingpolyethylene terephthalate resin that has physical and chemicalproperties that make it particularly well suited for filament-formingpurposes.

In general, the preparation of highly polymeric linear polyester resinfrom a dicarboxylic acid and a diol is well-known in the art. In thepreparation of such polyesters, a dicarboxylic acid and diol are firstcombined and subjected to a direct esterification reaction. Theresulting product or prepolymer is then polycondensed at highertemperatures and under reduced pressure in the presence of apolycondensation catalyst to form the desired polyester resin.

For commercial purposes, it is essential that the polyester resin beproduced in the shortest possible time and that the desired degree ofpolymerization be obtained. Additionally, it is essential that thepolyester resin be of such color so that filaments formed therefrom willappear substantially white in color. In particular, a polyethyleneterephthalate resin suitable for melt spinning should have a carboxylcontent value of about or below 50 equivalents per million grams (eq./l0gr. or meq./ kg.), an intrinsic viscosity of preferably not less than0.60 (as determined in a 60% phenol and 40% tetrachloroethane solution,wt./wt., at C.), a melting point preferably not less than about 258-260C., and be either pale white or off-white in color in order for thefilaments formed therefrom to possess a satisfactory level of hydrolyticstability, thermal stability, ultra-violet light stability, color andhave a high degree of tenacity.

It is an object of this invention to prepare a polyester resin by adirect esterification reaction between a diol and a dicarboxylic acid,followed by the polycondensation of the resulting esterified product.

Another object of the present invention is to provide a novel method forthe preparation of polyethylene terephthalate resin having excellentproperties and particularly suitable for melt extrusion intonon-degraded processable filaments by a direct esterification andpolycondensation reaction procedure.

Another object of the present invention is to provide an improved methodfor carrying out the direct esterification reaction between ethyleneglycol and terephthalic acid in the preparation of polyethyleneterephthalate.

These and other objects are accomplished in accordance with the presentinvention which involves a method of preparing polyethyleneterephthalate wherein terephthalic acid and ethylene glycol are directlyesterified and the product of esterification is polycondensed in thepresence of a polycondensation catalyst, the improvement comprising outthe said direct esterification reaction in the presence of a catalyticamount of an arsenic compound wherein the arsenic constituent thereof inits anionic form is neutralized properly by a basic cation constituentthereof.

In accordance with the present invention, it has been found thatarsenates and arsenites having a basic cation constituent areparticularly valuable as first stage additives or catalytic additives inthe first stage or direct esterification reaction between terephthalicacid and ethylene glycol, in the preparation of polyethyleneterephthalate. For example, among the first stage or catalytic additivesthat can be used in accordance with the present invention are ammoniumarsenate, diammonium arsenate, calcium arsenate, lithium arsenate,sodium arsenate, disodium methyl arsenate, sodium dimethyl arsenate,calcium arsenite, potassium hydrogen arsenite, sodium arsenite, anddisodium arseno-acetate monohydrate, or any combination thereof.

The subject arsenic compounds used as catalytic additives in the presentinvention are generally employed in the range of from about 5 l0 toabout 5X10 mole per mole of terephthalic acid in the subjectterephthalic acid-ethylene glycol reaction mixture. Higher or lowerconcentrations of the present catalytic additives can also be used.However, when concentrations less than the above are used, theircatalytic effort is generally reduced, whereas when concentrationsgreater than this are used, no further improvement in the desiredproduct is generally obtained.

The preparation of polyesters of the present invention via the directesterification reaction are generally carried out with a molar ratio ofethylene glycol to terephthalic acid of from about 1:1 to 15:1, butpreferably from about 1.221 to 2.521. The first stage directesterification reaction of the present method is generally carried outat temperatures ranging from about 220290 C. in the absence of anoxygen-containing gas at atmospheric or elevated pressure for about 2 to4 hours. For example, the reaction may be carried out in an atmosphereof nitrogen. When the direct esterification step is completed, asindicated, for example, by the formation of a clear reaction mixture,any remaining glycol is distilled off and a polycondensation catalyst isadded to the reaction product. The second stage or polycondensation stepof the present method is generally carried out under reduced pressure inthe range of from about 0.05 to 20 mm. of mercury in the absence of anoxygen-com taining gas at temperatures from about 260325 C. for about 2to 5 hours.

The polycondensation step of the present method is accomplished throughthe use of a conventional polycondensation catalyst, for exampleantimony trioxide. The polycondensation catalyst may, if indicated, beadded to the present reaction mixture before initiating the directesterification reaction between the diol and dicarboxylic acid or afterthe esterified reaction product thereof is formed. The polycondensationcatalysts are employed in concentrations ranging from about 0.005 toabout 0.5%, based on the total weight of the reactants.

In order to illustrate the excellent color of the resin which isobtained by using the method of the present invention, the reflectanceof the resins produced in the following examples were measured by aColor-Eye (Model D-l), which is the trade name for a diiferentialcolorimeter manufactured by the Instrument Development Laboratories,Attleboro, Mass. The color values obtained are based on luminance (Y onthe C.I.E. system), which is a measurement of the proportion of theincidence light reflected and therefore a measure of the whiteness orlightness of the polyester polymer being evaluated. The determination ofY on the 6.1.13. sys tem, as hereinafter set forth, was determined byusing a molded plaque of the polyester resin product having thedimensions 1" x 1" x A In general, it is considered that a polymer resinexhibiting a Y value of not less than about 40 out of a theoreticalpossible 100 under the present test conditions, is suitable for fiberforming purposes.

The following examples of several preferred embodiments will furtherserve to illustrate the present invention. All parts are by weightunless otherwise indicated.

EXAMPLES A mixture of terephthalic acid and ethylene glycol at ratiosand weights indicated in the following table, and X mole of a firststage arsenic compound additive, as listed in the following table withexact weight used, was charged to a Fischer-Porter pressure assemblyequipped with a nitrogen sparge tube and a distilling arm. The reactorwas lowered into an oil bath maintained at 260 C. or 270 C. and flushedfor ten minutes with dry nitrogen. All of the examples were initiallycarried out in a 260 C. oil bath, except Examples 3 and 4, which werecarried out in a 270 C. oil bath. A nitrogen pressure of 60 psi. wasapplied and a distillate of water-ethylene glycol was collected. When aclear reaction mixture, i.e. solution, was obtained, pressure wasreduced to atmospheric and the remaining glycol was distilled. Then, theresulting low molecular weight prepolymer was further reacted(polycondensed) in the presence of 0.04%, based on the weight of theprepolymer, of antimony trioxide under a vacuum of about 0.1 mm. ofmercury at 282 C. for periods of time indicated on the following tableto form a polyester resin.

The following table sets forth conditions and results of variousreactions carried out as described above.

turn, the polyester resin product. The present first stage additives actto reduce the direct esterification time and bring about the formationof a prepolymer which is, in general, characterized as being a morehighly esterified product than one wherein no esterification additive isused, as indicated by the carboxyl content values of the prepolymers. Inaddition, the prepolymers of the present method can be condensed withconvenional polycondsensation catalysts to yield polyester resins whichhave high molecular weights, as indicated by their intrinsicviscosities, low carboxyl content values, suitably high melting pointsand exceptionally good color, so as to make the resins particularlysuitable for filament-forming purposes.

The process of the present invention has been described with particularreference to polyethylene terephthalate. However, it will be obviousthat the subject invention includes within its scope the preparation ofother polymethylene terephthalates prepared from glycols of the seriesHO(CH OH, where n is 2 to 10 and terephthalic acid and copolyesterscontaining various amounts of other dicarboxylic acids, such asisophthalic acid.

We claim:

1. In a method of preparing polyethylene terephthalate resin whereinterephthalic acid and ethylene glycol are directly esterified and theproduct of esterification is polycondensed in the presence of apolycondensation catalyst, the improvement comprising carrying out thesaid direct esterification reaction in the presence of a catalyticamount of a direct esterification catalytic additive selected from thegroup consisting of ammonium arsenate, diammonium arsenate, disodiummethyl arsenate, sodium dimethyl arsenate, calcium arsenite, potassiumhydrogen arsenite, sodium arsenite, and disodium arseno-acetatemonohydrate.

2. The method of claim 1 wherein the arsenic compound is present in anamount ranging from about 5 X l0- to about 5 10 mole per mole ofterephthalic acid in the reaction mixture.

3. The process of claim 1 wherein the arsenic compound is ammoniumarsenate.

4. The process of claim 1 wherein the arsenic compound is sodiumdimethyl arsenate.

TABLE Molar ratio 1 of Pre- Weight of ethylene Esterifipolymer Polycon-Polyester first stage glycol to cation carboxyl deusatinn carboxylExample additive, terephtime, content, time, li'ltliIlSlG content,Melting Color Y No. First stage additive gms. thalic acid hrs. :minmam/kg. hours viscosity meqJkg. Pt... C. 0 .LE 1 None 2:1 3:41 316 40.36 32 2 Amngnium arse-hate (NHQ 0096 2:1 3:00 100 4 0. 30 258 49. 6

AS 4. 3 Diammonium arsenate 0088 L 5:1 3:00 125 4 1. 0 27 258 46. 9

(NH3)2HA.SO4. 4 Calfiitn arsenate Ca (AsO4) 0226 1. 5:1 3:00 15 2. 5 0.81 41. 9

3 z Lithium arsenate Li As04 0080 2:1 3:15 200 4 0. 91 42. 8 Sodiumarsenate Na As04 0104 1.2:4 2:30 4 0. 98 54. 7 7 Disodium methylarseuate 0092 2:1 3:00 4 O. 75 34 54. 2

NfigCHgASOs. 8 Sodium dimethyl arsenate 0107 2:1 3:30 4 0. 60 37Na(OHa)2AsOz-3H 0. 9 Calcium arsenite Ca (As0a)2. 0183 2: 1 3:30 150 20. 89 28 261 45. 5 10 Potassium hydrogen arsenite 0127 1. 5: 1 4:30 1684 0. 85 45 261 47. 5

KB (AsO 2) z 11 Sodium arsenite Na-AsOi 0065 1. 5: 1 3:00 4 0. 85 26 42.2 12 Disodium arseno-acetate 0123 1. 5:1 4:30 4 0. 94 21 261 43. 0

monohydrate (H0) (NaO) AsO CHiOO Na-HQO.

i In the above examples, where a 12:1 molar ratio terephthalic acid werepresent in the reaction mixture; acid were present; where a. 2: 1

2 No polycondensation catalyst added.

The intrinsic viscosities of the polyester resin products of the aboveexamples were determined in a 60% phenol and 40% tetrachloroethanesolution, wt./wt., at 30 C. The other analytical values set forth in theabove table were obtained by conventional laboratory procedures.

The results shown in the above table indicate that the presence of thearsenic compounds of the present method during the direct esterificationstep facilitates the prepof ethylene glycol to terephthalic acid isindicated, where a 1.5: 1 molar ratio is indicated, molar ratio isindicated, about 62 g. of ethylene glycol and 84 g. of terephthalic acidwere present in the reaction mixture.

about 47 g. of ethylene glycol and 103 g. or about. 53.4 g. of ethyleneglycol and 96.6 g. of terepht-halic 5. The process of claim 1 whereinthe arsenic compound is sodium arsenite.

6. The process of claim 1 wherein the arsenic compound is disodiumarseno-acetate monohydrate.

7. The process of claim 1 wherein the direct esterification catalyticadditive is diammonium arsenate.

8. The process of claim 1 wherein the direct esterificaaration of andimproves the prepolymer formed and, in 75 tion catalytic additive isdisodium methyl arsenate.

6 9. The process of claim 1 wherein the direct esterifica- FOREIGNPATENTS tion catalytic additive is calcium arsenite.

10. The process of claim 1 wherein the direct esterifica- 1297516 5/1962France' tion catalytic additive is potassium hydrogen arscnite. WILLIAMH. SHORT, Primary Examiner References Cited 5 LOUISE P. QUAST, AssistantExaminer UNITED STATES PATENTS Us CL 2,437,232 3/1948 Rothrock et a1.26075 260475 P0403" UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3 .496, 145 Dated February 11 I 1 970 Inventor(s)Mary E. Carter and John A. Price It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 2, line 7, after the word "comprising" insert the word carrying-;line 33, "effort" should be --effect-. Co1.3, line 11, "polymer" shouldbe --polyester-. In the Table, Example 3, under "First stage additive""(NH should be SIGNED AND SEALED JUN 2 319)) Anew wmrm n. saaumm, m.Amati! moor flomissiom of Patents

